The morphological basis of the armor-like folded skin of the Greater Indian Rhinoceros as a thermoregulator

The armor-like folded skin of the Indian rhinoceros (Rhinoceros unicornis) was examined by CT image analyses and microscopic observation. The three-dimensional reconstructed images demonstrate that the folded skin has the subcutaneous tissues including cutaneous muscles and connective tissues inserted to the deepest holes and grooves of 2–3 mm thickness in each fold. The cutaneous muscles are well-developed in subcutaneous tissues, in which many small blood vessels are found. We conclude that the folded skin acts as a thermoregulator, since the thin blood vessels and capillaries and cutaneous muscles in the subcutaneous tissues transmit the thermal energy from the core region of the body to the skin folds. We suggest that the greater Indian rhinoceros, Rhinoceros unicornis, has evolved the extraordinary thermoregulation mechanism in the folded skin adapted to high temperature in the tropical and subtropical regions.